Television radial scanning system employing cathode beam



ay 13, 1941. L. DE FOREST TELEVISION RADIAL SCANNING SYSTEM EMPLOYING CATHODE BEAM Filed July 13, 1957 2 Sheets-Sheet 1 INVENTOR. Lee d2 Fin/ eal ATTORNFVS May 13, 1941. 1. DE FOREST 2,241,899

TELEVISION RADIAL SCANNING SYSTEM EMPLOYING CATHODE BEAM Filed July 13, 1957 2 Sheets-Sheet 2 INVENTOR Le e e Ft) 496 1 BY &

ATTORNEYS Patented May 13, 1941 TELEVISION RADIAL SCANNING SYSTEM EMPLOYIN G CATHODE BEAM Lee de Forest, Hollywood, Calif., assignor to Ruth C. Gilman, Waterbury, Conn.

Application July 13, 1937, Serial No. 153,333

12 Claims.

This invention relates to improvements in television scanning systems and particularly to improvements in so-called radial scanning systems such as I have shown .in principle in my Patents Nos. 2,163,749, issued June 2'7, 1939, and 2,122,456, issued July 5, 1938. In said patents I have described certain types of mechanical radial scanning devices. The present invention is directed to the application of a cathode beam in place of a beam of light reflected from and directed by a mirror. Y

In the drawings,

Figure 1 is a side elevation, partly in section and partly diagrammatic, of a cathode ray tube together with associated apparatus for producing a radial scanning pattern;

Figure 2 is a cross-section along the lines 2--2 of Figure 1, looking in the direction of the arrows;

Figure 3 is a cross-section along the lines 3--3 of Figure 1, looking in the direction of the arrows and indicating the shape of the scanning pattern;

Figure 4 is a detailed diagrammatic view illustrating the actual scanning pattern which is obtained by my invention;

Figure 5 is a side elevation, partly diagrammatic, illustrating a modification of the apparatus of Figure 1 in which a plurality of defiestion plates are used for rotating the plane of the cathode beam by electrical means instead of by mechanical means as in Figure 1;

Figure 6 is a diagrammatic view of the apparatus which is to be associated with that shown in Figure 5, together with a modification of the cathode ray tube and electrode arrangement shown in Figure 5;

Figure 7 is a diagrammatic view illustrating the possibility of securing a rectangular picture with the apparatus disclosed in this application;

Figure 8 is a diagrammatic view illustrating an improved method of securing a photo-electric mosaic surface;

Figure 9 is an enlarged view further illustrating my improved photo-electric mosaic surface;

Figure 10 is a cross-section of the structure of Figure 9; and

Figure 11 is a further modification of the apparatus illustrated in Figures 1, 5 and 6.

In Figures 1 and 2 I have shown a conventional type of cathode ray tube l having an elongated cylindrical portion and an enlarged funnel-shaped portion. The tube contains a hot cathode 3, a tubular anode 4, and a perforated diaphragm 5. Between the diaphragm 5 and the enlarged funnel-shaped portion of the tube, I use two diametrically opposite narrow deflection plates 6, I, located on the outside of the tube as shown. Each of these plates is fixed to the inner end of an insulating radial arm, the outer ends of which are attached to the inside rim of a pulley 8. Attached to these radial arms are two collector rings M, iii, upon the outside surface of which rest contact brushes l2, l3. Each ring is connected to one of the deflection plates 6, 'l. The cathode tube is rigidly mounted on supports, not shown, and the pulley 8, together with the two radial arms, deflection plates 6 and l, and collector rings It and I5, is supported on four idler rollers r, r, in such a way that it is free to rotate about the axis of the stationary cathode beam tube. The pulley B is driven by a motor 19 by means of a belt or chain l7 and pulley it.

Each of the brushes l2, i3 is connected, as shown in Figure 1, to the terminals of the secondary 9 of a high voltage transformer, the primary ill of which is connected to the output of a sinusoidal alternating current source having a frequency of several thousand per second.- By this arrangement I cause the cathode beam to be deflected back and forth in a plane coincident with the midpoint of the two opposite deflection plates 6, l, at a frequency determined by that of the alternating current supply. Thus as the two deflection plates are rotated the plane of deflection of the cathode beam is likewise caused to rotate, with the result that the path of the cathode beam spot over the enlarged end of the tube traverses an approximately radial pattern as indicated in Figures 3 and 4.

The actual scanning pattern obtained with all of the modifications of the apparatus described herein is illustrated in Figure 4 from which it is seen that successive radial excursions of the beam do not repeat the previous path but are displaced slightly, thus filling in the scanning pattern. It is also to be noted that the pattern produced may be interweaved as illustrated and described in connection with Figure 9 of my Patent No. 2,122,456.

In Figures 5 and 6 I show an arrangement whereby the rotation of the plane of cathode beam deflection about the center axis of the tube is maintained by electrical instead of by mechanical means. With this arrangement I employ four, six, or more deflection plates arranged either within the glass wall of the tube shown in Figure 6 or without this glass wall as shown in Figure 5. These plates are preferably upon or near the point where the conical portion of the tube Joins the cylindrical portion thereof. In Figure 6 I show six such deflection plates from 86 to II mounted within the tube, each with a lead brought out through the wall of the tube. Each of said leads is connected to a corresponding sector I6 to 8| of a stator, which sectors are mounted in the form of a circle, in the center of which is located a rotating shaft, preferably the projection of the shaft of the driving motor. This shaft carries two opposite radial arms of insulating material. On the outer end of each arm is mounted a curved sector 2|, 22, covering an arc approximately equal to one-sixth of the circumference of the circle and so located that these two sectors travel in close proximity to but out of contact with the fixed stator sectors. To the two radial arms are mounted two collector rings l4, I5, each connected to one rotor plate and upon which rest two brushes l2, l3. These brushes are connected to the two terminals of the secondary 9 of a high voltage transformer, the primary H) of which is connected to the output terminals of the last stage of a voltage amplifier. In the input circuit of this amplifier is a sinusoidal alternating current supply of, say, five thousand cycles.

By the arrangement here described I am thus able to produce a radial scanning pattern either over the large end of the cathode beam tube as shown in Figure 1 or over a specially prepared (fluorescent or photo-electric) plane surface S, Figures and 11.

A cathode beam radial scanning device such as I have here described is of particular advantage for use as a pickup device or camera at a television transmitter. Such a camera maybe used to record an image which is to be reproduced on a much larger scale and therefore the size of the reproduced image is not restricted by the size of the cathode ray tube.

In using my device as a camera, I locate in the enlarged portion of the cathode beam tube a photo-electric mosaic surface. The structure, composition and methods of. forming such a photo-electric mosaic surface are now well known in the art and require no detailed description here except as regards an improved method of forming such a surface which will be hereinafter described. The original idea of a photo-electric mosaic surface swept by a cathode beam to serve as a television camera or pickup device was first suggested and described by Mr. Cambell- Swinton of England many years ago.

This photo-electric mosaic surface may be dethe glass or mica is located the photo-electric mosaic S.

In Figure 11 I have shown a somewhat different shape of the cathode beam tube and a somewhat different arrangement of the elements of the photo-electric surface within the enlarged portion of the tube. The arrangement is such that a reduced image of the object 48 may be thrown directly upon the mosaic surface S through a plane or nearly plane clear window located in the conical portion of, the cathode beam tube. The photo-electric mosaic may be deposited upon the front surface S of a large disc of mica or glass, on the back surface of which is attached or deposited a relatively thick conducting metallic surface S to which the conductor 83 leading to the input of the television amplifier is attached and makes firm contact.

posited upon the inside spherical surface at the .effecting an electrical connection between the surface S which constitutes an outer condenser plate of the photoelectric system to the input stage of the first amplifier of the television pickup system.

In Figures 1 and 5 I have shown a photographic lens so located as to throw a light image of the object to be televised upon the conducting transparent surface S while on the inside surface of It will, of course, be obvious that electromagnetic instead of electro-static means for defleeting the cathode beam may be employed.

Where it is desired to transmit a rectangular picture instead of one of circular form the sensitive photo-electric mosaic surface is confined to said rectangular form, illustrated in Figure 7 as a square, by the simple expedient of masking off the four arcual areas as they are here shown. Or the same result may be obtained by modulating the high frequency beam-deflecting potentials to conform to the secantial form in a manner disclosed in my two patents above referred to.

I have devised a novel method of forming the photo-electric mosaic surface, as a result of which certain advantages and regularity as regards the exact form and area of the individual photoelectric elements are obtained. Figure 8 shows one type of this improved structure and process. Here F is a corner portion of a supporting frame for the mosaic structure. This structure consists of a woven fabric of exceedingly fine thread, such as rayon, fine silk, or spun quartz, shown here as woven in a simple square pattern. This fabric is first dipped in a thin lacquer or insulating varnish of such constituency as to shrink when drying and leave small circular apertures in the squares formed by the warp 30 and woof 3| of the fabric. This result may be facilitated by tightly stretching the fabric in its frame, dipping it into the insulating solution, and then exposing the fabric to a blast of air which blows away the surplus fluid, leaving round holes 32 as shown in Figure 9. When this structure is properly dried the photo-electric material may be sprayed or deposited upon the same in sucha manner as to fill only the interstices formed in the fabric as above described.

A crosssection of this fabric is shown in Figure 10. The back of the fabric is then coated with a thin dielectric material, suchas Bakelite, enamel or lacquer, which latter when dried may be coated by sputtering or spraying processes with a conducting layer of metal, for'example silver, aluminum, or the like. This is illustrated at 33 in Figure 10. In lieu of coating the back of a fabric with dielectric material the fabric may be placed against a thin sheet of mica, quartz, or glass, and against the back of said insulating material may be placed or deposited a sheet or foil of suitable metal. Or after the conducting photo-electric material 32 has been deposited in the spaces between the threads of the fabric, the back of the fabric may be made conductive as by spraying or sputtering without the intervention of a di-electric layer between the two. In this case I have a multiplicity of photo-electric cells, each one insulated from the others around its edges yet each directly connected to a common conducting backing or surface layer. This arrangement ofiers certain advantages over that heretofore used, where only a capacity relation exists between the individual photo-electric cells and the common conducting layer or area.

What I claim is:

l. A cathode beam tube, means causing the beam to swing back and forth in one plane through a common center point, and means for causing said plane to rotate continuously through 360 about its mid-axis.

2. A cathode beam tube, a plurality of defleeting plates arranged at the periphery of said tube, a source of alternating current potential, and means for impressing said potential on said plates in succession at a rate which is slow compared to the frequency of said alternating current potential whereby the cathode beam is caused to traverse successive radial paths through a common center point.

3. A cathode beam tube, a plurality of deflecting plates arranged at the periphery of said tube,

a source of alternating current "potential, and

means for impressing said potential on said plates in succession at a rate which is slow compared to the frequency of said alternating current potential whereby the cathode beam is caused to traverse successive radial paths through a common center point, said radial paths being continually changed in a regular and uniform manner.

4. A cathode beam tube, a plurality of pairs of electrodes, a source of alternating voltage, and means for applying said voltage to said pairs of electrodes successively at a rate which is slow compared to the frequency of said voltage, whereby there is set up in said tube a continuously rotating electro-static field of alternating current potentials of frequency many times higher than the rate of rotation, and the cathode beam traverses successive paths cutting the central axis of the tube.

5. A cathode beam tube, means for deflecting the beam in a plane passing through the axis of said tube, and means for continuously rotating said plane of sweep through 360 around said axis at a rate which is slow compared with the speed of deflected movement of said beam.

6. A cathode beam tube, means for deflecting the beam in a plane passing through the axis of said tube, means for rotating said plane of sweep around said axis, and means for limiting the sweep of said beam so that the end of said beam reverses its sweep at points which lie upon the boundary of a rectangle.

'7. A cathode beam tube, means for rapidly deflecting the beam in a plane passing through the axis of said tube, means for continuously slowly rotating said plane of sweep through 360 around said axis, and means for limiting the sweep of said beam.

8. A cathode beam tube, a photo-electric surface therein, means for causing said beam to swing back and forth through a common center point in one plane, and means for causing said plane to rotate continuously through 360 about its midaxis, whereby said beam is caused to traverse said surface in successive radial paths.

9. A cathode beam tube, means causing the beam to swing back and forth in one plane, means for causing said plane to rotate continuously through 360 about its mid-axis at a rate which is slow compared to the rate of swing of said beam,

and means for causing the swings of said beam to be at harmonic velocity.

10. A cathode beam tube, means comprising deflection plates and a source of alternating current sine wave potential for deflecting the beam through the axis of said tube, and means for continuously rotating said plane of sweep around said axis.

11. A cathode beam tube, a surface therein responsi've to said beam, means for causing said beam to traverse said surface in successive radial paths through a common center, which paths are continuously displaced through 360, and means for causing the rate of traversal to be harmonic.

12. A cathode beam tube, means for deflecting the beam in a plane passing through the axis of said tube, and means for continuously rotating said plane of sweep through 360 at a speed which difiers greatly from the speed of deflected movement of said beam.

LEE n2 FOREST. 

